If your using a computer as one of the tools for your work, it might be advisable to use a laptop rather than a desktop computer.

The laptop you can conveniently put into a burglar-proof safe for security, whereas a desktop ..... .

Use as much password protection as possible to protect your work.

You might find it necessary to run multiple operating systems on your computer to gain a suitable degree of protection.

The less anyone knows about the computer hardware and software tools your using, the more difficult its going to be for your work and computer equipment to be modified.

You'll find that friends and relatives can be quite glib and informative when discussing their "inventor" friend.

The more information saboteurs have before entering your working environment, the more preparation they can make and the less time their nefarious activities will  [ require ] ; i.e. the smaller the likelihood they'll be caught.

If, while working on your computer, you discover errors recurring in your work that you've previously corrected, your computer is being got to in some way or another.

The newer files containing the work are being downloaded and replaced with older files of the work with the file date adjusted.

Using a CD-Recording system - most manufactures offer parallel port versions - to permanently store you files in a non-overwrite form should eliminate this particular problem.

Large capacity, removable magnetic storage disks with password protection also offer some protection against this vulnerability; however, such a disk can be re-formatted, and rewritten regardless its password protection.

Your comment on using the disk after this type of tampering might be:

" Damn! I'm getting careless. 

I put this disk away without password protection."

Encrypt your files before storage.
Using reasonably price public key encryption software^40a to protect all your files affords further protection for your computer work.

This type of encryption software also permits more secure E-mail and other type correspondence.

Encryption also permit's the viable and inexpensive use of the PTO Disclosure Document Program to legally establish the date of invention for your work.

Encrypt your work, print out the encrypted work (ASCII armored), and use the printout as your disclosure document (DD).

You can then submit via the U.S. mail a Disclosure Document which you might otherwise need to hand carry to the PTO.

If and when you file your patent application, you'll need to make available to the patent examiner the software and keys necessary to decrypt your DD. 

Hopefully, the examiner will tolerate this minor inconvenience.

You might check with your patent attorney on the acceptability of the [topic] methodology.